摘要:

Structure and properties of 5‐epi‐flavoxanthin and 5‐epi‐chrysanthemaxanthinThe absolute configurations of 5‐epi‐flavoxanthin (6) and 5‐epi‐chrysanthemaxanthin (7) prepared by acid catalysed rearrangement of semi‐synthetic lutein epoxide5are shown to be (3S, 5S, 8R, 3′R, 6′R) and (3S, 5S, 8S, 3′R, 6′R), respectively. Contrary to published data [5] the relationship of the polyene chain and H3(18) on the dihydrofurane ring iscisfor the pair of stereoisomers having a Δδ = δ (HC(7)) − δ (HC(8)) = 0,22 ppm and3J ≡ 0. These conclusions are in

ISSN:0018-019X    

DOI:10.1002/hlca.19780610502

出版商:WILEY‐VCH Verlag GmbH    

年代:1978

数据来源: WILEY

摘要:

Macrocyclic and noncyclic neutral ionophores. Effect of the macrocyclic ring on the ion selectivityA series of macrocyclic 3, 6‐dioxaoctanedioic diamides was prepared. Their ion selectivity in membranes was compared with nonmacrocyclic analogues. The ion selectivity as well as the capability to extract ions from aqueous solutions to an organic phase decreases with decreasing ring siz

ISSN:0018-019X    

DOI:10.1002/hlca.19780610503

出版商:WILEY‐VCH Verlag GmbH    

年代:1978

数据来源: WILEY

摘要:

Influence of the lipophilicity of 3,6‐dioxaoctanedioic diamides on their ion carrier propertiesA series of lipophilic 3,6‐dioxaoctanedioic diamides (potential ionophores for Ca2+) have been prepared. With increasing lipophilicity the ionophoric behavior of these ligands vanishes. This loss is shown to be due to kinetic limitations in the exchange reactions between aqueous phase and membrane ph

ISSN:0018-019X    

DOI:10.1002/hlca.19780610504

出版商:WILEY‐VCH Verlag GmbH    

年代:1978

数据来源: WILEY

摘要:

Oscillating Chemical Reactions. 11. Behaviour of the “induction period” in the BrO 3−/Ce4+/Cyclohexanon and BrO 3−/Ce4+/Cyclopentanon systems(1)The addition of α‐monobromoketone, one of the products of reaction of the BrO3−/Ce4+/Cyclohexanon (S1) and BrO3−/Ce4+/Cyclopentanon (S2) oscillating systems, decreases and even suppresses the induction period (τind.) in the case ofS2.Such is not the case withS1: τind.increases and the oscillations can even be completely inhibited.(2)The order of addition of the reagents and the time lapse (tadj.) preceding the addition of the last of them influences τind., particularly when the last reagent added is Ce4+.(3)In our experimental conditions, the inhibition of the oscillatory phenomenon by Cl−ions is definite only for | Cl−| ≥ 5,0 · 10−2M (S1) and |Cl−|>2,5 · 10−3M (S2); for lower concen

ISSN:0018-019X    

DOI:10.1002/hlca.19780610505

出版商:WILEY‐VCH Verlag GmbH    

年代:1978

数据来源: WILEY

摘要:

Electrochemical Formation of Δ1,2‐NorborneneThe electrochemical reduction of 1,2‐dihalogen norbornanes in tetrahydrofuran/furan leads to a mixture of two isomeric cycloadducts6and7. The ratio of these adducts corresponds to those which have been found in reductive bisdehalogenation of1and2by butyllit

ISSN:0018-019X    

DOI:10.1002/hlca.19780610506

出版商:WILEY‐VCH Verlag GmbH    

年代:1978

数据来源: WILEY

摘要:

Study of the flavonic and xanthonic compounds in the leaves ofGentiana ciliataL.Fifteen 1,3,7,8‐oxygenated xanthones (1–15) were isolated from the leaves ofGentiana ciliataL. (genusGentianopsis). Among these were six new glycosides: glucosyl‐1‐decussatin6, glucosyl‐1‐gentiacaulein (8), primeverosyl‐8‐isogentiacaulein (9), glucosyl‐3‐isogentiacaulein (10), glucosyl‐1‐swertianin (12) and primeverosyl‐7‐swertianin (13). Three known flavone C‐gluco

ISSN:0018-019X    

DOI:10.1002/hlca.19780610507

出版商:WILEY‐VCH Verlag GmbH    

年代:1978

数据来源: WILEY

摘要:

AbstractThe general reactivity of various sites in the vindoline series has been investigated. The facility of electrophilic substitution at C(15) and the effect of steric crowding on reactions at C(4) are discussed. At the basic nitrogen sites, oxidations with mercuric acetate and potassium permanganate are also discussed.

ISSN:0018-019X    

DOI:10.1002/hlca.19780610508

出版商:WILEY‐VCH Verlag GmbH    

年代:1978

数据来源: WILEY

摘要:

A synthetic model of the active site of the coenzyme B12dependent methylmalonyl‐CoA mutaseThe synthesis of a bridged cobaloxime with a built‐in methylmalonic ester moiety is described. 2‐Brommethyl‐2‐methylmalonic acid dichloride (5) afforded upon reaction with 5‐heptin‐1‐ol (4) the corresponding diester6. Subsequent treatment of6with ozone, dimethylsulfide and hydroxylamine hydrochloride led to the pentadentate ligand: 10‐brommethyl‐10‐methyl‐9, 11‐dioxo‐8, 12‐dioxa‐nonadecane‐2, 3, 17, 18‐tetraone tetraoxime (8). Reaction of8with cobalt (II) chloride, pyridine and sodium borohydride furnished in 7% yield the bridged cobaloxime10, which was spectroscopically characterized. Short term irradiation of10in methanol caused the exchange of the axial pyridine ligand by a solvent molecule affording10a, the structure of which has been determined by X‐ray crystallography. Long term irradiation of10in methanol or ethanol led to irreversible cleavage of the Co, C‐bond. Upon alkaline hydrolysis the degradation product afforded methylsuccinic acid in 82–95% yield. No incorporation of solvent protons into this product could be observed. Implications of these findings for the mechanism of the coenzyme‐B12catalysed rearr

ISSN:0018-019X    

DOI:10.1002/hlca.19780610509

出版商:WILEY‐VCH Verlag GmbH    

年代:1978

数据来源: WILEY

摘要:

AbstractThree kinds of polar substitutent effects are observable in the solvolyses of 1‐R‐substituted 3‐bromoadamantanes (VI). This follows from the relationship between products, rate constantskin 80% ethanol, and the inductive substituent constants σ 1qof the substituent R. Alkyl groups and electron‐attracting substituents at C (1) control the rate by their inductive effects alone, since logkcorrelates closely with σ 1q. However, rates are higher than predicted on the basis of the respective σ 1qvalues when conjugating (+M)‐substituents or electrofugal groups are attached to C(1). These exalted substituent effects are attributed to CC‐hyperconjugative relay of positive charge from the cationic center at C(3) to the substituent at C(1). When the substituent is a strong electron donor (e.g.O−and S−), accelerated substitution gives way to heterolytic fragmentation, rates and products then being controlled b

ISSN:0018-019X    

DOI:10.1002/hlca.19780610510

出版商:WILEY‐VCH Verlag GmbH    

年代:1978

数据来源: WILEY

摘要:

“Push‐Pull” Acetylenes as Reagents for Peptide SynthesisA series of ‘push‐pull’ acetylenes 1 is easily available from the corresponding “push‐pull” olefins by a simple bromination‐dehydrobromination sequence. The versatility of the acetylenes with regard to peptide syn

ISSN:0018-019X    

DOI:10.1002/hlca.19780610511

出版商:WILEY‐VCH Verlag GmbH    

年代:1978

数据来源: WILEY